.TH std::num_put::put,std::num_put::do_put 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::num_put::put,std::num_put::do_put \- std::num_put::put,std::num_put::do_put

.SH Synopsis
   Defined in header <locale>
   public:

   iter_type put( iter_type out, std::ios_base&
   str,

                  char_type fill, bool val ) const;
   iter_type put( iter_type out, std::ios_base&
   str,
                  char_type fill, long val ) const;
   iter_type put( iter_type out, std::ios_base&
   str,                                                     \fI(since C++11)\fP
                  char_type fill, long long val )
   const;
   iter_type put( iter_type out, std::ios_base&
   str,
                  char_type fill, unsigned long val
   ) const;
   iter_type put( iter_type out, std::ios_base&
   str,                                                     \fI(since C++11)\fP
                  char_type fill, unsigned long
   long val ) const;
   iter_type put( iter_type out, std::ios_base&
   str,
                  char_type fill, double val )
   const;
   iter_type put( iter_type out, std::ios_base&
   str,
                  char_type fill, long double val )
   const;
   iter_type put( iter_type out, std::ios_base&
   str,
                  char_type fill, const void* val )
   const;
   protected:                                       \fB(1)\fP

   virtual iter_type do_put( iter_type out,
   std::ios_base& str,

                             char_type fill, bool
   val ) const;
   virtual iter_type do_put( iter_type out,
   std::ios_base& str,
                             char_type fill, long
   val ) const;
   virtual iter_type do_put( iter_type out,
   std::ios_base& str,                                                    \fI(since C++11)\fP
                             char_type fill, long
   long val ) const;
   virtual iter_type do_put( iter_type out,
   std::ios_base& str,
                             char_type fill,            \fB(2)\fP
   unsigned long val ) const;
   virtual iter_type do_put( iter_type out,
   std::ios_base& str,                                                    \fI(since C++11)\fP
                             char_type fill,
   unsigned long long val ) const;
   virtual iter_type do_put( iter_type out,
   std::ios_base& str,
                             char_type fill, double
   val ) const;
   virtual iter_type do_put( iter_type out,
   std::ios_base& str,
                             char_type fill, long
   double val ) const;
   virtual iter_type do_put( iter_type out,
   std::ios_base& str,
                             char_type fill, const
   void* val ) const;

   1) Public member function, calls the protected virtual member function do_put of the
   most derived class.
   2) Writes characters to the output sequence out which represent the value of val,
   formatted as requested by the formatting flags str.flags() and the std::numpunct and
   std::ctype facets of the locale imbued in the stream str. This function is called by
   all formatted output stream operators, such as std::cout << n;.

   Conversion occurs in four stages:

.SH Stage 1: conversion specifier selection

     * I/O format flags are obtained, as if by

   fmtflags basefield = (str.flags() & std::ios_base::basefield);
   fmtflags uppercase = (str.flags() & std::ios_base::uppercase);
   fmtflags floatfield = (str.flags() & std::ios_base::floatfield);
   fmtflags showpos = (str.flags() & std::ios_base::showpos);
   fmtflags showbase = (str.flags() & std::ios_base::showbase);
   fmtflags showpoint = (str.flags() & std::ios_base::showpoint);
     * If the type of val is bool:
          * If boolalpha == 0, then converts val to type int and performs integer
            output.
          * If boolalpha != 0, obtains
            std::use_facet<std::numpunct<CharT>>(str.getloc()).truename() if val ==
            true or std::use_facet<std::numpunct<CharT>>(str.getloc()).falsename() if
            val == false, and outputs each successive character c of that string to out
            with *out++ = c. No further processing is done in this case, the function
            returns out.
     * If the type of val is an integer type, the first applicable choice of the
       following is selected:
          * If basefield == oct, will use conversion specifier %o
          * If basefield == hex && !uppercase, will use conversion specifier %x
          * If basefield == hex, will use conversion specifier %X
          * If the type of val is signed, will use conversion specifier %d
          * If the type of val is unsigned, will use conversion specifier %u
     * For integer types, length modifier is added to the conversion specification if
       necessary: l for long and unsigned long
       , ll for long long and unsigned long long
       \fI(since C++11)\fP.
     * If the type of val is a floating-point type, the first applicable choice of the
       following is selected:
          * If floatfield == std::ios_base::fixed, will use conversion specifier %f
          * If floatfield == std::ios_base::scientific && !uppercase, will use
            conversion specifier %e
          * If floatfield == std::ios_base::scientific, will use conversion specifier
            %E

     * If floatfield == (std::ios_base::fixed |
       std::ios_base::scientific) && !uppercase, will use conversion
       specifier %a                                                       \fI(since C++11)\fP
     * If floatfield == (std::ios_base::fixed |
       std::ios_base::scientific), will use conversion specifier %A

     * If !uppercase, will use conversion specifier %g
     * Otherwise, will use conversion specifier %G
   Also:
     * If the type of val is long double, the length modifier L is added to the
       conversion specifier.
     * If the type of val is a floating-point type
       and floatfield != (ios_base::fixed | ios_base::scientific)
       \fI(since C++11)\fP, the precision modifier is added and set to str.precision().
       Otherwise, no precision is specified.
     * For both integer and floating-point types, if showpos is set, the modifier + is
       prepended
     * For integer types, if showbase is set, the modifier # is prepended.
     * For floating-point types, if showpoint is set, the modifier # is prepended.
     * If the type of val is void*, will use conversion specifier %p
     * A narrow character string is created as if by a call to std::printf(spec, val)
       in the "C" locale, where spec is the chosen conversion specifier.

.SH Stage 2: locale-specific conversion

     * Every character c obtained in Stage 1, other than the decimal point '.', is
       converted to CharT by calling
       std::use_facet<std::ctype<CharT>>(str.getloc()).widen(c).
     * For arithmetic types, the thousands separator character, obtained from
       std::use_facet<std::numpunct<CharT>>(str.getloc()).thousands_sep(), is inserted
       into the sequence according to the grouping rules provided by
       std::use_facet<std::numpunct<CharT>>(str.getloc()).grouping()
     * Decimal point characters ('.') are replaced by
       std::use_facet<std::numpunct<CharT>>(str.getloc()).decimal_point()

.SH Stage 3: padding

     * The adjustment flag is obtained as if by std::fmtflags adjustfield = (flags &
       (std::ios_base::adjustfield)) and examined to identify padding location, as
       follows:
          * If adjustfield == std::ios_base::left, will pad after
          * If adjustfield == std::ios_base::right, will pad before
          * If adjustfield == std::ios_base::internal and a sign character occurs in
            the representation, will pad after the sign
          * If adjustfield == std::ios_base::internal and Stage 1 representation began
            with 0x or 0X, will pad after the x or X
          * Otherwise, will pad before
     * If str.width() is non-zero (e.g. std::setw was just used) and the number of
       CharT's after Stage 2 is less than str.width(), then copies of the fill
       character are inserted at the position indicated by padding to bring the length
       of the sequence to str.width().

   In any case, str.width\fB(0)\fP is called to cancel the effects of std::setw.

.SH Stage 4: output

   Every successive character c from the sequence of CharT's from Stage 3 is output as
   if by *out++ = c.

.SH Parameters

   out  - iterator pointing to the first character to be overwritten
   str  - stream to retrieve the formatting information from
   fill - padding character used when the results needs to be padded to the field width
   val  - value to convert to string and output

.SH Return value

   out

.SH Notes

   The leading zero generated by the conversion specification #o (resulting from the
   combination of std::showbase and std::oct for example) is not counted as a padding
   character.

   When formatting a floating point value as hexfloat (i.e., when
   floatfield == (std::ios_base::fixed | std::ios_base::scientific)), the \fI(since C++11)\fP
   stream's precision is not used; instead, the number is always printed
   with enough precision to exactly represent the value.

.SH Example

   Output a number using the facet directly, and demonstrate user-defined facet:


// Run this code

 #include <iostream>
 #include <locale>

 // this custom num_put outputs squares of all integers (except long long)
 struct squaring_num_put : std::num_put<char>
 {
     iter_type do_put(iter_type out, std::ios_base& str,
                      char_type fill, long val) const
     {
         return std::num_put<char>::do_put(out, str, fill, val * val);
     }

     iter_type do_put(iter_type out, std::ios_base& str,
                      char_type fill, unsigned long val) const
     {
         return std::num_put<char>::do_put(out, str, fill, val * val);
     }
 };

 int main()
 {
     auto& facet = std::use_facet<std::num_put<char>>(std::locale());
     facet.put(std::cout, std::cout, '0', 2.71);
     std::cout << '\\n';

     std::cout.imbue(std::locale(std::cout.getloc(), new squaring_num_put));
     std::cout << 6 << ' ' << -12 << '\\n';
 }

.SH Output:

 2.71
 36 144

   An implementation of operator<< for a user-defined type.


// Run this code

 #include <iostream>
 #include <iterator>
 #include <locale>

 struct base { long x = 10; };

 template<class CharT, class Traits>
 std::basic_ostream<CharT, Traits>&
     operator<<(std::basic_ostream<CharT, Traits>& os, base const& b)
 {
     try
     {
         typename std::basic_ostream<CharT, Traits>::sentry s(os);

         if (s)
         {
             std::ostreambuf_iterator<CharT, Traits> it(os);
             std::use_facet<std::num_put<CharT>>(os.getloc())
                 .put(it, os, os.fill(), b.x);
         }
     }
     catch (...)
     {
         // set badbit on os and rethrow if required
     }

     return os;
 }

 int main()
 {
     base b;
     std::cout << b;
 }

.SH Output:

 10

   Defect reports

   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.

     DR    Applied to          Behavior as published              Correct behavior
                      the bool overload used non-existing     use these members of
   LWG 34  C++98      members                                 std::numpunct
                      truename and falsename of std::ctype
                      the precision modifier was only added
   LWG 231 C++98      if                                      removed these conditions
                      (flags & fixed) != 0 or str.precision()
                      > 0
   LWG 282 C++98      the thousand separators were only       also inserted for
                      inserted for integral types in stage 2  floating-point types

.SH See also

   operator<< inserts formatted data
              \fI(public member function of std::basic_ostream<CharT,Traits>)\fP
